Well its not dead yet, just not booting up correctly, its powering up ok you said.
Perhaps corrupted fw maybe? on the motherboard.
What type of flash card (where did you get it?, its not an old dspdb vmail one is it?)
Have you got another exifu card you can try?
You don't need the LAN obviously for the Exifu but wonder if its working, if you try and boot up (leave for a few mins) with normal switch ON, insert flash card to the exifu - do you get the red LED coming on (exifu) to indicate insertion?
What is the fault with the previous ccu? Could you possibly use the psu/chassis from replacement and motherboard from original failed unit